The invention relates broadly to a combination of encapsulation, immobilization and release of active material using hydrogel microbeads, where the active can be either water soluble or water insoluble. Specifically, the hydrogel microbeads immobilize encapsulated agricultural chemicals such as pheromones, herbicides, insecticides and pesticides, whereby the encapsulated active material is released into ambient air by diffusion through at least two paths sections: a microcapsule shell and a hydrophilic matrix.
Methods of eliminating unwanted pests from orchards, crops and forests frequently entail the use of organophosphate insecticides. Alternative methods involve insect mating disruption, where insect pheromones are used to control pests and protect agricultural crop. In insect mating disruption methods, the mating pheromone plume of a female insect is typically masked with other pheromone point sources. This reduces the likelihood of a male insect finding a female, and subsequently disrupts and reduces larvae production. The insect population of the next generation is thus decreased, as well as potential crop damage.
Conventional sprayable pheromone formulations are generally provided in liquid filled microcapsules containing an active. Typically, the microcapsules have a polyurea membrane that can be formed using an interfacial process involving an isocyanate and an amine. Microencapsulation by this method has been described for example in U.S. Pat. No. 4,487,759 (Nesbitt et al, 1984). These polyurea membranes allow actives to be released into the atmosphere for up to a total of 2-3 weeks for most insect pheromones. Membranes of polyurea capsules are generally semi-permeable, therefore active material can diffuse across the membranes and release slowly with time. Potentially, high concentrations of active in the air can be observed immediately upon delivery or spraying of encapsulated products. This may be attributable to a high occurrence of capsule bursts or potential leaks in microcapsules.
U.S. Pat. No. 4,532,123 teaches capsules containing a pharmaceutical active material in primary capsules, that are further encapsulated within a second membrane to create secondary capsules. The intracapsular liquid core of the secondary capsules contain enzymes which slowly hydrolyze the membrane of the primary capsules. This slow hydrolysis enables the slow release of active from the primary capsules into the larger capsular core for controlled delivery.
A Japanese paten, JP 8-173794 teaches encapsulation of an amine within small capsules of polymethyl methacrylate membranes. These capsules are further encapsulated within an epoxy-amine polymeric shell. Similarly, the amine within the tiny capsules is released into the core of the larger capsule ultimately delivering the amine upon rupturing of the polymeric shells.
Use of interfacial condensation to encapsulate substances such as pharmaceuticals, pesticides and herbicides is taught in U.S. Pat. No. 3,577,515. The encapsulation process involves two immiscible liquid phases (typically water and an organic solvent), one being dispersed in the other by agitation, and the subsequent polymerization of monomers from each phase at the interface between the bulk (continuous) phase, and the dispersed droplets. Polyurethanes and polyureas are materials suitable for producing the microcapsules. The microcapsules comprising a polymeric sphere and a liquid centre, ranging from 30 micron to 2 mm in diameter, depending on monomers and solvents used.
Highly viscous and thickened hydrogels have been used to deliver pheromones, fragrances and other non-water soluble actives. U.S. Pat. No. 4,755,377, for example, describes a process of encapsulating perfume or fragrant material within an aqueous-based gel composition. The resulting material is in the form of a highly viscous semi-solid. U.S. Pat. No. 5,645,844 describes the use of chitosan paste for delivery of pheromones to disrupt insect mating, where the material can be dispensed by an apparatus such as a caulking gun. Due to their thickness and high viscosity, these materials, however, are generally unsprayable compositions.
Most hydrogels are safe and non-toxic to humans. Hydrogels have been used for the encapsulation of biological materials whereby the formulation is non-lethal to the viability of the cells, proteins, and related materials. U.S. Pat. No. 4,689,293, describes the process of encapsulating living tissue or cells. The encapsulation shell permits the passage of materials and oxygen to the cells and permits the diffusion of the metabolic by-products from the gel.
To provide an extended release period of an active, microbeads comprising a hydrophilic matrix with active-filled microcapsules entrained therein is provided. The hydrophilic matrix is capable of immobilizing a broad spectrum of microencapsulated active materials, either water soluble or non-water soluble. The microbeads may be suspended in a sprayable solution.
In an aspect of the invention, the hydrophilic matrix may be made from a water soluble matrix-forming material to provide an environmentally friendly microbead.
In a further aspect of the invention, the microbeads may be capable of rehydrating after an initial dehydration and release of active. Thus, the release and longevity of the active can be controlled by adjusting the humidity of the environment in which the microbeads have been delivered.